1. Field of the Invention
This invention relates generally to remote range finding apparatuses and methods and more particularly to an apparatus and method for accurate ranging in adverse weather conditions.
2. Description of the Related Art
Radar range finding instruments such as military and domestic aircraft monitoring installations and maritime vessel tracking and docking assistance systems typically do not have major problems seeing through atmospheric weather patterns. However, these same instruments do not have high accuracy or resolution such as accuracy to within a meter of the target object.
Laser range finding instruments, also known as LIDAR instruments (light distancing and ranging), on the other hand, are highly accurate but the light pulse can be reflected and distorted by adverse weather conditions such as fog, rain and snow. Consequently, laser range finding instruments are not normally used in adverse weather conditions.
Accordingly, both radar systems and laser systems have been used independently and together to monitor maritime vessel docking operations. One such system is marketed by Laser Communications Incorporated, a subsidiary of Laser Technology, Inc., 7070 S. Tucson Way, Englewood, Colo., the assignee of the present invention. This conventional system utilizes a laser range finder backed up by a radar range finder, both mounted on the vessel dock and aimed in the direction of vessel approach. Both the laser range finder and the radar systems are operated simultaneously, typically with the radar system providing a backup reference which is subservient to the laser system and thus not actively utilized. Its output data is recorded and stored for later comparison with the laser system results if needed. The radar system is not used for actual docking unless there is a problem with the laser system or substantial fog blocks the laser light pulses. In this latter instance, the laser system cannot distinguish a target vessel from the fog reflections and thus the only reliable indication of distance and vessel approach speed is provided by the radar system. A mobile vessel docking aid system incorporating both laser and radar systems is disclosed in copending U.S. application Ser. No. 08/788,426, Jan. 28, 1997, hereby incorporated by reference in its entirety.
During adverse weather conditions such as rain and fog, the accuracy of the conventional vessel docking aid systems is reduced because the laser ranging information is not usable and the less accurate radar ranging data must be used to provide distance and approach speed information. This accuracy is highly desirable to prevent excessive approach speeds of extremely large vessels. Accordingly, there is a need for a more accurate means of obtaining this information.